Transistors made in whole or in part of organic materials can be less expensive and easier to manufacture than traditional transistors and can be used in applications where traditional transistors are not economical and high density is not required. For example, organic transistors could be used for electronic paper, posters and books, smart cards, toys, appliances and electronic bar codes for product identification. Organic transistors can also be made from flexible materials, and such transistors can be used to control diodes in flexible panel displays for computers, laptops and televisions.
The performance of TFT devices is typically characterized by examining the behavior of the “on” current (Isd) measured in a regime where the source/drain voltage is larger than the gate voltage. Here the current, known as the saturation current, is independent of the source/drain voltage and can be related to other characteristics of the device according to Equation 1:
                              I          sd                =                              W                          2              ⁢              L                                ⁢          C          ⁢                                          ⁢                                    μ              ⁡                              (                                                      V                    g                                    -                                      V                    T                                                  )                                      2                                              (                  Equation          ⁢                                          ⁢          1                )            where μ is the effective mobility of the semiconductor and C is the capacitance of the gate dielectric, which in turn is proportional to the dielectric constant ε of the dielectric layer. Vg is the gate voltage and VT is the threshold voltage. Transistors that have large “on” currents possess some combination of large μ, high ε, and high C. The TFT output current is linearly dependent on the capacitance, proportional to the dielectric constant of the dielectric layer and inversely proportional to its thickness. Driving the transistor at low voltages requires either a very thin pinhole-free dielectric, or alternatively, a thicker dielectric with a high dielectric constant.
To be useful in a TFT, the dielectric layer must be fairly thin (˜1 micron), possess a suitable ε, and be essentially pinhole-free. At minimum, the dielectric must fully insulate the gate from the source and drain. A process is needed to create such dielectric layers with high-resolution features in a cost-effective manner.